Effects of Chemical Lesioning the Dorsal or Rostral Ventrolateral Medulla on Glutamate-induced Cardiovascular Actions of the Pontine Gigantocellular Tegmental Field and Lateral Tegmental Field of the

Abstract

The present project studies the effects of chemical lesioning in the dorsal medulla (DM) or rostral ventrolateral medulla (RVLM) on glutamate-induced cardiovascular action of the pontine gigantocellular tegmental field (PFTG) and lateral tegmental field (PFTL) in cats. Experiments were performed on 39 adult cats anesthetized with intraperitoneal injection of a mixture of alpha-chloralose and urethane. Systemic arterial blood pressure (SAP), heart rate (HR) and vertebral nerve sympathetic activity (VNA) were continuously monitored. Microinjections of the glutamate solution (Glu, 0.25 M of sodium glutamate dissolved in artificial cerebrospinal fluid with 0.5% pontamine sky blue) in 50- to 70- nl aliquots were made in the PFTG and PFTL. SAP, HR, and VNA were measured before and after chemical lesioning of the DM and/or RVLM and compared. The DM or the RVLM was lesioned by injection of 150-200 nl of kainic acid (24 mM) acutely. We found that when the ipsilateral DM was lesioned, microinjection of Glu into PFTG no longer elicited a pressor response. In contrast, when the contralateral DM was lesioned, the Glu-induced PFTG pressor response was little affected. Lesioning of either the ipsi- or contralateral RVLM affected the PFTG response very little. This suggests that the connection between PFTG in producing the pressor action is principally unilateral through the ipsilateral DM. When the ipsi- or contralateral DM was lesioned, injection of Glu into the PFTL no longer could elicit a depressor response. Interestingly, when either the ipsi- or contralateral RVLM was lesioned, the PFTL-induced depressor effect changed to a pressor one. These results suggest that the PFTL depressor effect is dependent on the integrity of both the DM and RVLM. Furthermore, there may be a mixture of sympathoexcitatory and parasympathoexcitatory neurons in the PFTL.